Back in the 1960s, a beautifully simple picture emerged. Our DNA consisted of recipes for proteins. The double helix could be unzipped to allow RNA copies of these recipes to be made and sent to the protein-making factories in cells. But by the 1970s, it had become clear that only a tiny proportion of our DNA codes for proteins - just 1.2 per cent, we now know. What about all the rest? Some assumed it must do something, others suggested it was mostly junk. "At least 90 of our genomic DNA is 'junk' or 'garbage' of various sorts," the geneticist Susumu Ohno wrote in 1972. Ohno knew, though, that some of the DNA that didn't code for proteins still played a vital role. For instance, the process of making RNA copies of genes - transcription - involves clusters of proteins binding to specific sequences near the genes. These proteins - called transcription factors - control the activity of genes by either boosting or blocking transcription, so the sequences to which they bind are known as regulatory DNA or switches. So how much DNA acts a switch, or has some other function? To provide an overall picture of which parts of the genome do what, the Encyclopedia of DNA Elements (ENCODE) project was set up in 2003. It involves many teams around the world using a variety of techniques. The results of a pilot study looking at just 1 per cent of the genome were released in 2007. This week, the results of its study of the entire genome were released, with the publication of more than 30 papers in Nature and other journals. Among other things, ENCODE looked for switches that control gene activity. The researchers did this by taking known transcription factors and seeing which bits of DNA these proteins bound to. So far, they have found 4 million sites, covering 8.5 per cent of the genome - far more than anyone expected.